Hoop structures and various other components with annular-shaped sections at times must be diametrically expanded to attain or restore desired diametrical conditions, such as during the manufacturing or reconditioning of shrouds and nozzle supports of gas turbine engines. For relatively ductile materials, sizing can be accomplished by hydraulic expansion methods while the component is at or near room temperature ("cold sizing"). However, a component can be susceptible to tensile fractures during cold-sizing if formed from certain materials, including superalloys commonly employed in gas turbine engines. For these materials, sizing must be performed at an elevated temperature. One such method is generally referred to as hot creep sizing, and involves a high mass fixture with a coefficient of thermal expansion (.alpha.) that is relatively constant for the temperatures used and equal to or higher than the structure being sized. A difficulty with hot creep sizing is the requirement for slow and tightly controlled heating and cooling rates in order to match the growth of the fixture with the component being sized, which slows processing throughput. Another thermal creep-sizing method is known as warm sizing, and involves expanding a preheated component on a mandrel that is maintained at a lower temperature throughout the sizing operation. With many materials including superalloys, the component must be heated to very high temperatures, e.g., 1800.degree. F. (about 980.degree. C.) or more, which may pose a hazard to the operator.
In view of the above, it would be desirable if an improved method were available for sizing a hoop structure that avoided the disadvantages of prior art methods.